The invention is directed to a process and a device for measuring a throttle point according to the generic part of the independent claims.
Conventionally, mechanical or optical measuring methods are used when measuring throttle points, especially bore holes, nozzles or diaphragms, but these methods are difficult to use when the throttle points to be measured are very small. This necessitates the development of new procedural methods such as those known, e.g., from DE-OS 196 36 431. This reference is concerned with a process and a device for testing the operability of a tank ventilation installation, the process being based on the following principle: pressure is applied to the tank ventilation installation by means of a pressure source, with the pressure resulting in the tank or vessel being proportional to one of the operating characteristic quantities or parameters of the pump. If the vessel or the tank ventilation installation has a leak, a correspondingly different pressure results, .which in turn affects one of the operating parameters of the pressure source, e.g., current, voltage and/or rotational speed. By detecting or acquiring these operating parameters, conclusions can be drawn as to whether a leak is present in the vessel. By comparison with a suitable reference leak, a decision can be made as to whether the detected leak is bigger or smaller than the reference leak. A qualitative measurement of this leak is carried out; however, a quantitative determination of the magnitude of the leak is not possible.
The process according to the invention with the features of the main claim has the advantage of being not only a qualitative but also a quantitative method for measuring a throttle point, especially a bore hole, nozzle, diaphragm or a leak. Through acquisition and storage of at least one operating parameter of the pump and through additional acquisition and storage of at least two reference operating parameters of two reference throttles, it is possible to make a quantitative statement about the magnitude of a throttle by comparing the operating parameter with reference operating parameters which can be saved in an evaluating unit.
Advantageous further developments of the process according to the main claim are made possible by the measures indicated in the subclaims.
It is accordingly advantageous when at least one reference operating parameter of one reference throttle is determined before the throttle point to be measured, since before the actual measurement or measurements take place a calibration, that is, a correlation of operating parameter to throttle magnitude, can be carried out or a check can be carried out as to whether the system has changed with respect to an earlier calibration, or whether this earlier calibration can still be used.
If at least two reference operating parameters are determined before the throttle point to be measured, it is possible to output the magnitude of the actual throttle point directly after measuring it and thus to make a direct determination.
If the process is used within the framework of automated production processes, where the emphasis is on the highest possible piece number of throttles identical to each other, it is exceedingly advantageous when the reference operating parameters are acquired only once and then used for the comparison of a plurality of throttle points to be measured. In this manner, their magnitude can be determined very quickly in a correspondingly time-saving manner, since the reference data are already known and alternating measurement of the reference throttle and actual throttle is therefore dispensed with.
The actual physical principle of this process is based on a comparison of the pressure prevailing at a reference throttle and the pressure prevailing at a throttle point to be measured. Since measuring the pressure necessitates additional technological steps, acquiring the operating parameters of the pump instead is known to be of great advantage; this is because there is generally a proportional relationship between them and the resulting pressure. Appropriate operating parameters of a pump are the current flowing through the pump, the voltage applied to the pump or the rotational speed of the pump. Naturally, in order to obtain measurements that are correct and can be reproduced, the operating parameters are advisably only measured when a constant backpressure has built up at the reference throttle or the throttle to be measured.
It can also be advantageous when the process is configured in such a way that the reference throttles can be measured in a separate arm or branch of the measuring arrangement. In this manner, reference throttles and throttle points to be measured can be exchanged independently of each other. This can be. especially advantageous if the magnitude of a throttle point to be measured can not easily be estimated in advance and there is accordingly no hint of which size reference throttle should ideally be used. If, on the other hand, a reasonable estimate of the geometry of the throttle points to be measured is possible and there is accordingly no foreseeable need for complicated reference measurements, it can be advantageous to measure the reference throttles in the same place as the throttle points to be measured. In this case, a switching mechanism between the corresponding branches of a measuring arrangement is no longer necessary.
Differing geometries of reference throttles and throttle points to be measured can lead to inaccuracies in the measurement results. For this reason, it is advantageous when evaluating to correct the operating parameters or the reference operating parameters, or both, with a correction factor and/or an addition term. In this manner, this process, which is to be realized by a machine that uses a determined set of reference throttles, can be used for a wide variety of geometries of different throttle points to be measured.
Determining the throttle magnitude can either be done via an averaging process or a logical comparison or by matching a characteristic curve to the reference operating parameters. The latter is advantageous because it increases the accuracy of the process. An additional increase of the accuracy of this process can be achieved by measuring as many reference throttles as possible.
Another advantageous variant of this process consists in that the evaluation of the measurement results is effected using a reference characteristic curve stored in the processing unit. This allows the measuring of a large number of throttle points without having to go back explicitly to the reference throttles. Therefore, it is also advantageous to store a plurality of reference characteristic curves in the evaluating unit, which makes it possible to switch between different geometries of throttle points to be measured without problems and without previous calibration. This is a particularly user-friendly variant of the process which permits the omission of complicated and possibly lengthy calibrating measurements.
There is a variety of possible embodiment forms of a corresponding device for realizing the claimed process. A device that calculates and outputs the throttle magnitude as quickly as possible and in an automated fashion is especially desirable and therefore especially advantageous. Accordingly, it is conceivable that, in addition to the obligatory second reference throttle for the quantitative determination of the throttle point to be measured, there is an evaluating unit containing at least a storage for receiving the operating parameters and storage for receiving the reference operating parameters. The throttle point magnitude can then be calculated on the basis of these stored values using a logical unit. This logical unit must accordingly be connected to the storage units as well as to an output device for outputting the calculated result.
Further, it is advantageous when there is a storage for storing reference characteristic curves.
The use of a vane-cell pump is especially advantageous because, in this pump, there is a very precise relationship between the pressure and the operating parameters, especially the current flowing through the motor of the pump. This precise relationship enables a correspondingly high accuracy of measurement.
For switching to at least one branch of the measuring arrangement which can be acted upon by fluid under pressure, a wide variety of valves could be used. Magnet valves have proven to be an advantageous means of switching.
It is moreover highly advantageous when the data supplied to the evaluating unit is in digitized form. This is achieved by the use of suitable analog-to-digital converters; this also gains the additional advantage of making the entire set of data available to other machines working on a digital basis.